Washington — A Senate bid to sanction China over trade abuses cleared its highest hurdle Thursday morning with a bipartisan, supermajority vote and seemed on track for passage by Friday morning, at the latest.

Then came a move so unexpected that, for a time, it left senators fixed in their seats, stunned, and silent.

At 6:38 p.m. on Thursday, majority leader Harry Reid (D) of Nevada pulled what’s known in the Senate as “the nuclear option” – cutting off Republicans from offering amendments to pending bills.

Indeed, some Republicans say that, going forward, they will block all legislation, unless Democrats change the rule to cut off amendments. With Democrats needing Republican support to bring bills to the floor, that could essentially bring the chamber to a legislative standstill for the foreseeable future.

Some Democrats offered a more hopeful prognosis, suggesting that the move could shock Republicans and Democrats into addressing deeper rifts that have divided them and made the Senate part of the broader congressional dysfunction. But in the cloistered world of the Senate, Reid's move was a seismic event that could create ill will not easily overcome.

Business as usual, until...

In short, it came about because Reid simply became tired of Republicans proposing amendments at least partly aimed at hurting Democrats in the next election.

Democrats say that GOP obstructionist tactics are now so pervasive that the Senate barely functions, requiring the majority leader to plan the legislative calendar around filing cloture motions to limit debate. Republicans counter that amendments are one of the minority's most powerful legislative levers – their last shot at influencing what’s debated on the floor.

By 6:38 p.m. Thursday, the tourists had gone home, and the galleries were empty. A vote to end debate on the China trade measure – called a cloture vote – had passed earlier on Thursday with 12 Republican votes, 62 to 38. From that point on, the bill’s passage was virtually certain.

Leaders on both sides of the aisle had agreed to allow seven amendments, which represented business as usual.

The issue is a sensitive one for Democratic senators in farm states. They don't want to be seen as voting against the Obama administration's environmental regulations, but the rule is seen as draconian among farmers. Reid knew that the vote was a no-win situation for his farm-state senators – and the Republicans had offered it precisely for that reason.

So Reid said, essentially, enough is enough and denied the switch.

Republicans responded by turning to a ploy that has long precedent in the Senate: suspending the rules so they could bring up amendments without the consent of the majority.

What Reid did next has thrown the Senate into turmoil.

What Reid did

In a move not vetted with GOP leaders or most Democrats on the floor, Reid, reading from a script, called on the Senate to end that precedent by simple majority vote.

Reid defended himself. “The same logic that allows for nine such motions could lead to the consideration of 99 such amendments,” he said. “This practice has gotten way out of hand … and that is a result that a functioning democracy cannot tolerate.”

But Republicans were astonished. Instead of rushing to the airport after the last vote before a weekend, more than half the Senate stayed in their seats to talk publicly about the meaning of the vote they had just taken. The mood was sober, unscripted, and highly attentive.

“Members on both sides of the aisle feel like this institution has degraded into a place that is no longer a place of any deliberation at all,” said Sen. Bob Corker (R) of Tennessee.

In 2005, the then-Republican majority famously considered a similar move after minority Democrats filibustered President Bush’s judicial nominations to a standstill. Not having the 60 votes needed to break the filibuster, the Republicans challenged the ruling of the chair that the Democrats were well within their rights. The vote to overrule the chair – who is advised by the Parliamentarian, the Senate's adviser on its own rules – required only a majority.

Democrats at the time called this the "nuclear option" – a legislative trick to get around the need for a 60-vote majority in the Senate.

Senator Reid, then the minority whip, called the tactic “very un-American.”

“The political damage would be done to Republicans for many years to come,” he said in a floor speech on April 21, 2005. “This is something we should work out. This is something that should not cause the disruption and dysfunction of our family, the Senate family.”

A deal was eventually worked out.

Is the Senate at a breaking point?

Today, it's uncertain what comes next. Senate Republicans, speaking after Thursday’s vote, say that the right of the minority to bring up amendments is as important as the right to filibuster or debate without limit.

Reid "wants to run the Senate like he’s king,” Sen. Mike Johanns (R) of Nebraska, author of the farm-dust amendment, told reporters off the floor.

“The price of being the majority is you have to take bad votes, because in the United States Senate the minority is entitled to be heard – not entitled to win, but entitled to be heard,” said Senator McConnell.

Before now, Reid has repeatedly blocked amendments before cloture. Thursday's decision to block amendments after cloture, too, means “the minority’s out of business,” he added. “And it’s particularly bad on a big bill that has the support of over 60 members, as this one did.”

McConnell got some support from Democrats. “I agree with the minority leader … the deal around this place is the majority sets the agenda and the minority gets to offer amendments,” said Sen. Charles Schumer (D) of New York, who is charged with policy and messaging for the Democratic caucus.

“If we’re going to bring this place back to a way where we can legislate, we are going to have to have both sides back off, and we’re going to have to figure out how to do that,” he added. “We need a little bit of a cooling off period.”

GOP aides say that strong feelings over the “nuclear option” won’t change the final vote on the China currency bill, which now needs only a majority vote to pass. But the president’s jobs bill, also scheduled for a vote requiring a 60-vote “supermajority” will fall short, with all Republicans and likely a few Democrats voting in opposition.

“They just changed this history of the Senate,” said Sen. Tom Coburn (R) of Oklahoma, who predicts that Republicans will be reluctant to agree to take up any bill in the future, without a prospect of proposing amendments.

Most senators exiting the chamber some two hours after the vote, described the process as confusing, sobering, but perhaps, eventually, helpful.

“We listened to each other,” said Sen. Dianne Feinstein (D) of California. “You could hear a pin drop. For the first time, there’s a glimmer of understanding and a possible way to a solution. It was a very significant evening.”